X-linked ichthyosis (XLI) is a hereditary disorder of the skin that affects males almost exclusively. Female carriers of the abnormal gene may occasionally demonstrate clinical findings. Corneal opacities (clouding of the clear part of the eyeball that overlies the iris) and cryptorchism (undescended testicles) are also commonly seen in patients with XLI. Ichthyosis (reddened, scaling skin) is caused by a deficiency of the enzyme steroid sulfatase. Individuals with XLI do not possess the gene for steroid sulfatase production.